Tensioners are usually implemented to compensate for geometrical variations in the belts of mechanical power transmissions of the kind including a belt passing over a driving pulley driven by an engine shaft and in turn driving at least one driven pulley. The wheel of such a tensioner is applied with pre-stress against the drive belt to minimize variations in the mechanical tension in the belt in spite of variations in the operating conditions of the engine over a relatively long period of time. By taking up static and dynamic lengthening of the belt, the tensioner avoids the belt sliding relative to the cheekplates of the driving or driven pulleys in a mechanical power transmission. Such a tensioner includes a wheel pressed against the belt and mounted to rotate about a first axis, the wheel support being capable of pivoting about a second axis that is separate from and parallel to said first axis. Resilient return means enable the wheel to induce mechanical tension in the belt to compensate for static and/or dynamic variations in the length thereof due in particular to cyclical irregularities of the engine while running, in particular when idling or during sudden changes generated by switching on and/or off devices that are driven by the shafts rotated by the pulleys of the mechanical power transmission.
A tensioner also includes damper means, in particular hydraulic damper means, or as described in French patent application No. 93 06898 an elastomer fitting for the wheel, in which case the elastomer fitting also acts as resilient return means pressing the wheel against the belt. Although the tensioner of French patent application No. 93 06898 provides the belt with a degree of damping against vibration, its static and dynamic performance as a tensioner are limited by the absence of resilient return means other than those provided by the elastomer covering. The use of such a tensioner is thus limited to small tensions and small variations in the length of the belt.
Unfortunately, the belt travelling under mechanical tension vibrates and transmits acoustic vibrations to the air, thereby generating noise which can be troublesome, particularly for the passengers of a motor vehicle when the belt is a transmission or distribution belt for a motor vehicle engine.